Ch 16- Evolution of Populations

1. Ch 16- Evolution of Populations • What are the main sources of heritable variation in a population? • Mutations and gene shuffling from sexual reproduction • Genetic variation= studied in populations • What is a population? • Gene pool- all genes, including different alleles, that are present in a population • Relative frequency- # of times that the allele occurs in a gene pool, compared to other alleles for same gene • Expressed as % • Nothing to do with allele being recessive or dominant • In genetic terms, evolution = any change in relative frequency of alleles in a population

2. Sources of Genetic Variation • Main sources of genetic variation= mutations and genetic shuffling from sexual reproduction • Mutations- any change in sequence of DNA • May affect organism’s fitness or ability to survive and reproduce • May have no effect on fitness • Gene shuffling- occurs during production of gametes • Crossing over • Sexual reproduction- major source of variation within many populations

3. Single-Gene and Polygenic Traits • What determines the numbers of phenotypes for a given trait? • Depends on how many genes control that trait • Single-gene trait- controlled by single gene that has two alleles • Widow’s peak • Polygenic trait- controlled by two or more genes • Two or more alleles • Many possible phenotypes and genotypes

4. Sec 2- Evolution as Genetic Change • Evolution- any change over time in the relative frequencies of alleles in a population • Populations evolve over time, not individuals • How does natural selection affect single-gene and polygenic traits? • On single-gene traits= can lead to changes in allele frequencies • Organism of one color may produce fewer offspring than organisms of other colors

5. Natural Selection on Polygenic Traits • Natural selection can affect the distributions of phenotypes by directional selection, stabilizing selection, disruptive selection • Directional selection- individuals at one end of curve have higher fitness than individuals in the middle or at end • Stabilizing selection- takes place when individuals near the center of curve have higher fitness than individuals at either end • Disruptive selection- individuals at the upper and lower ends of the curve have higher fitness than individuals near middle

7. Genetic Drift • Natural selection- not only source of evolutionary change • Genetic drift- random change in allele frequencies that happens in small populations • Individual with particular allele may leave more descendants than others, just by chance • Over time, series of chance occurrences of this type can cause allele to become common in population • May occur when small group of ind colonizes a new habitat • Founder effect- allele frequencies change as a result of migration of a small subgroup of a pop.

8. Evolution Versus Genetic Equilibrium • Hardy-Weinberg principle- allele frequencies in a pop will remain constant unless one or more factors cause those frequencies to change • Genetic equilibrium- allele frequencies remain constant • Conditions required to maintain genetic equilibrium • Random mating • Population must be large • No movement into or out of population • No mutations • No natural selection

9. Sec 3- Process of Speciation • Speciation- formation of new species • What must happen for a species to evolve into two new species? • Gene pools of two populations must become separated • Reproductive isolation- members of two pop cannot interbreed and produce fertile offspring • Behavioral isolation • Geographic isolation • Temporal isolation

10. Behavioral isolation- two populations have differences in courtship rituals or other reproductive strategies that involve behavior • Eastern and western meadowlarks • Geographic isolation- two pops are separated by geographic barriers, like rivers, mountains, bodies of water • Abert and Kaibab squirrel • Do not guarantee formation of new species • May separate some organisms but not others • Temporal isolation- two or more species reproduce at different times • Orchids in rain forest • Welcome to Discovery Education Player

11. Speciation in Darwin’s Finches • How did the process of speciation in the Galapagos finches occur? • Founding of a new population • Geographic isolation • Changes in new population’s gene pool • Reproductive isolation • Ecological competition

12. Why is understanding evolution important? • Drug resistance in bacteria and viruses • Pesticide resistance in insects • Evolutionary theory helps us understand and respond to these changes in ways that improve human life